Semiconductor wafers or other such substrates are typically subjected to many processing steps that involve moving a cassette of wafers from one type of apparatus to another. For example, wafers that have been subjected to one process in a vapor deposition chamber may have to be moved and cleaned and dried in other apparatus, and then transferred to a different apparatus for additional processing steps. It is very important that the wafers in process be kept isolated from contamination when being transferred. One technique that has been developed is to transfer them in a sealed box or pod. In the new location, it is then necessary to open the box to allow access to the wafers. To minimize contamination and to minimize labor requirements, the box is preferably opened robotically. A FOUP which is one such box has a front-opening door that can be removed by robotic equipment after the door frame has been sealed to mating equipment.
The cost of processing semiconductor wafers, always a prime consideration, is often evaluated by the throughput per unit of cost. Another measure is the throughput per area of floor space, which means that it is desirable to reduce the footprint of the apparatus employed. Related to both is the importance of reducing the capital cost of equipment. Inventions that can improve the competitive edge by either measure are highly desirable.